Use the following trick when you fight the Gobin King to take back the stolen food and spark plug for the motorcycle. Make sure the Boss is not on an Element Hex or it will refill his HP. Also, make sure you are not in an Element Hex or you cannot heal your party if they are in an Element Hex. Use Shut Out on Gobin King and shut out all the other Element Hexes so he cannot move there. Then, just use your basic attack and special attack on him until he has been defeated. Make sure you heal and are at least level 40 before fighting him.